This invention is generally concerned with a method and apparatus for testing an NVM and more particularly with methods and apparatus for identifying operational characteristics of an NVM.
Commercially available electronic postage meters are equipped with multiple non-volatile memory (NVMs) for redundantly storing critical data utilized in the course of operating the meter. For example, the serial number of the meter is preferably redundantly stored inasmuch as it is utilized for identifying the meter in the course of operation thereof when the meter is reset to store additional postage funds therein. In addition, data accounting for the total of postage funds available to be dispensed, and the total of all postage funds dispensed at any time, by the meter are normally stored in redundant NVM registers to ensure recovery, for example, after each power down cycle of the postage meter.
An additional step normally taken to guard against the loss of critical operational data is to use NVMs of different types from different manufacturers in the manufacture of the electronic postage meters. This step is taken to be sure that at least one of the redundant NVMs incorporated in each meter will survive in the event of a meter breakdown due to any eventuality, including for example, exposure to radiation, fire or physical destruction. Thus NVMs supplied by different suppliers of such products are preferably used for manufacturing each postage meter. On the other hand, different suppliers may provide NVMs having different operational characteristics, whether or not the per unit cost for each NVM is comparable. For example, a given supplier may provide NVMs which are byte-write-type NVMs, i.e., those which implement a programming mode of operation for storing a given byte of data immediately after the given byte is written thereto, whereas another supplier may provide NVMs which are page-write-type NVMs, i.e., those which implement a programming mode of operation for storing a predetermined number of bytes of data, say 16, 32 or 64 bytes, immediately after the predetermined number of bytes of data, known in the art as a page size, are written thereto.
Assuming the postage meter's electronic circuitry has been designed to use NVMs having a page size of 32 bytes, and not all NVM manufacturers provide that particular type of NVM and one or more selected manufacturers cannot timely provide a sufficient quantity of such NVMs to permit a given manufacturing run of postage meters to be completed, the timely manufacture of such postage meters is jeopardized. Accordingly, it is preferable that the electronic circuitry of the postage meter be designed to operate with byte-write-type or page-write-type NVMs, and that the page-write-type NVMs be those having any page size, i.e., 1, 16, 32, 64 or 128 byte page sizes, to provide for flexibility in choosing suppliers and accommodating changes in the availability of a sufficient number of NVMs at any given time. Moreover, in order to avoid a slow down in the manufacturing process by a postage meter manufacturer, and to take advantage of cost differentials which may be available from a given NVM supplier at any given time, it is preferable that the circuitry be designed to automatically accommodate and be operable with any available type of NVM.
Accordingly:
an object of the invention is to provide an improved postage meter; PA1 another object is to provide a method and apparatus for testing an NVM; and PA1 yet another an object is to provide an electronic circuit including means for testing a selected NVM to identify operational characteristics thereof.